In conventional steering wheels, the generally metallic skeleton comprises the hub region, the spokes and the steering wheel rim. In the hub region, high material strengths are necessary in order to be able to transfer all the forces occurring in the intended use of the steering wheel in as space-saving a manner as possible onto the steering column which is fastened in the vehicle body. Also the spoke and rim regions of the steering wheel skeleton must be designed primarily for the steering forces which are to be transferred. Furthermore, these regions of the steering wheel skeleton have already been designed for some time such that in the case of an impact of the driver of the vehicle caused by an accident, they can absorb a high proportion of the impact energy by deformation and hence reduce the risk of injury.
Steering wheel skeletons are either constructed from metallic semifinished parts which are preformed in a machining or non-machining manner and which are connected with each other by means of welding or soldering processes, or by a casting technique and then are generally produced in one piece from a light metal alloy. In so doing, of course one strives to meet all mechanical requirements with as small an expenditure of material as possible, the manufacturing methods by casting technique being in fact generally more expensive, but offering substantially more possibilities in fashioning compared with the manufacture from semifinished shaped parts.
A further essential aspect in the design of steering wheel skeletons results from the necessity of fastening the airbag module, which in all modern motor vehicles is arranged as standard in the steering wheel. With the explosion-like unfolding of the airbag, quite considerable reaction forces arise for a short period of time, which have to be transferred reliably from the airbag mount to the steering wheel skeleton.